The disclosure relates to an automatic transmission having a continuously variable transmission mechanism and a forward/backward switching device, more particularly to an automatic transmission having a first power transmission path provided via a forward/backward switching device and a second power transmission path provided parallel to the first power transmission path via a continuously variable transmission mechanism.
Conventionally, as an automatic transmission appropriate for, for example, a vehicle, there is a widely used automatic transmission having a belt type continuously variable transmission mechanism that has a pair of pulleys and a metal belt (or chain) wound around the pulleys and continuously varies the speed by changing the effective diameters of the pulleys. In addition, there is a known automatic transmission using a toroidal type continuously variable transmission mechanism, a cone ring type continuously variable transmission mechanism, or the like in addition to a belt type continuously variable transmission mechanism.
In addition, as such an automatic transmission, there is a developed automatic transmission having two parallel power transmission paths, which are a first power transmission path coupling the input shaft to the output shaft via a forward/backward switching device and a second power transmission path coupling the input shaft to the output shaft via a continuously variable transmission mechanism (see WO2013/176208). In the automatic transmission, the forward/backward switching device has a first clutch for forward travel and a brake for backward travel and a dog clutch is present in the first power transmission path and a second clutch is present in the second power transmission path.
In addition, the dog clutch is configured by a synchromesh mechanism including a first rotary shaft, disposed in the part of the first power transmission path on the forward/backward switching device side from the dog clutch, that operates together with the forward/backward switching device, a second rotary shaft, disposed in the part of the first power transmission path on the output shaft side from the dog clutch, that operates together with the output shaft, and a synchronizer sleeve (referred to below as the sleeve), provided concentrically with the first rotary shaft and the second rotary shaft movably in the shaft direction, that can mesh with the meshing portions of the first rotary shaft and the second rotary shaft. At least parts of the first rotary shaft and the second rotary shaft are formed as a double shaft overlapped in the shaft direction.
In the automatic transmission, when the vehicle starts traveling forward or travels forward at a speed less than a predetermined speed, a non-continuously variable mode is entered in which the first clutch and the dog clutch are put in the engagement state and the second clutch is put in the release state to travel at a forward low speed stage without performing a continuously variable speed change so that the driving torque from a driving source is transferred from the input shaft to the output shaft using the first power transmission path. Alternatively, when the vehicle travels forward at a speed equal to or more than the predetermined speed, the second clutch is put in the engagement state and the first clutch and the dog clutch are put in the release state to enter a continuously variable mode so that the driving torque from the driving source is transferred from the input shaft to the output shaft using the second power transmission path.